The invention relates to aftercoated pearl luster pigments and to a process for preparing them. The invention further relates to the use of these pigments.
EP 0 632 109 B1 discloses pearl luster pigments which for use in coating compositions are subjected to an aftertreatment in order to enhance their stability.
The pearl luster pigments known from EP 0 632 109 possess the following general layer sequence: the first xe2x80x9clayerxe2x80x9d is formed by the substrate, e.g. mica, the second layer is a metal oxide layer, e.g. titanium dioxide or iron (III) oxide, and these two layers form the base pigment. Atop the calcined base pigment, beginning with a third layer, the aftercoating, as it is known, is applied. The third layer comprises oxides, hydroxides and/or oxide hydrates of silicon, or aluminum, the fourth layer comprises oxides, hydroxides and/or oxide hydrates of silicon, aluminum, zirconium and/or cerium, and is different from the third layer, and the fifth layer comprises organofunctional coupling agents, e.g. silanes or zirconium aluminates.
Despite the stabilizing aftercoating of layers three to five described above, the pearl luster pigments, especially those based on mica and coated in the second layer with iron (III) oxide, are unsuitable for use in all fields, since under extreme stresses even higher stability of the pigments would be necessary.
Similar comments apply, in particular, to the mica-based pearl luster pigments coated in the second layer with titanium dioxide or other metal oxides, such as chromium oxide, zirconium dioxide, tin dioxide or zinc oxide; although they are in many cases more stable than the iron (III) oxide-coated micas, they likewise cannot be used without restrictions.
The aftercoated pearl luster pigments known from the prior art, furthermore, possess the disadvantage that their orientation in coating films is not optimal; in other words, an improvement in the parallel alignment of the pigments with respect to the film coat would be desirable in order to enhance the luster properties.
One of the features of the invention is to increase the stability of such pigments and to provide pigments which possess improved orientation within coating films.
This feature can be achieved in accordance with the invention by the provision of pigments having the following layer sequence:
a first layer, consisting of a platelet-shaped substrate,
a second layer,
comprising one or more metal oxides,
the first and second layers forming a calcined base pigment,
a third layer, comprising the corresponding uncalcined oxide, hydroxide or oxide hydrate of the oxide of the second layer,
a fourth layer, comprising oxides, hydroxides and/or oxide hydrates of silicon or aluminum,
a fifth layer, comprising oxides, hydroxides and/or oxide hydrates of silicon, aluminum, zirconium and/or cerium, this layer differing from the fourth layer, and
a sixth layer, comprising one or more organofunctional coupling agents.
The third layer in this sequence adopts the function of an adhesion promoter and embraces preferably from 0.1 to 10% by weight, more preferably from 1 to 5% by weight, and even more preferably 1-3% by weight, based on the base pigment.
Suitable platelet-shaped substrates for the base pigment are the substrates specified in EP 632 109 B1, such as mica, kaolin or glass, for example. Particular preference is given, however, to mica as the base substrate.
Preferably and optionally independently, the first layer has a thickness of 400-2000 nm. The second layer has a thickness of 50-300 nm, the third layer has a thickness of 5-30 nm, the fourth layer has a thickness of 10-50 nm, and the fifth layer has a thickness of 10-50 nm.
Suitable metal oxides of the second layer are, for example, iron (III) oxide and/or titanium dioxide or other metal oxides, such as chromium oxide, zirconium dioxide, tin dioxide or zinc oxide, and the oxides may also be present in mixtures. Preferred metal oxides include iron (III) oxide and/or titanium dioxide. Particularly high improvements over the pearl luster pigments known from EP 632 109 B1 are achieved in the case of the iron (III) oxide-coated substrates. Desirably, the second layer is 25-80% by weight with respect to the base pigment, i.e. first plus second layer.
Suitable organofunctional coupling agents are the coupling agents disclosed in EP 632 109 B1. They include, in particular, silanes, zirconium aluminates, zirconates or titanates, the silanes preferably possessing the structure Y-(CH2)n-SiX3 in which n is 2-8, Y is an organofunctional group, e.g. an amino, methacrylic, vinyl, alkyl, aryl, halogen and/or epoxy group, and X is a silicon-functional group which following its hydrolysis reacts with active sites of an inorganic substrate or by condensation with other silicon compounds. This group Y may comprise, for example a hydroxy, a halogen or an alkoxy group.
In addition to these substantially hydrophilic coupling agents, it is also possible to use hydrophilic silanes, especially the aryl-, alkyl- and fluoroalkyl- substituted di- and trimethoxysilanes. These include, for example, phenethyltrimethoxysilane, propyltrimethoxysilane, butyltrimethoxysilane, isobutyltrimethoxysilane, hexyltrimethoxysilane, octyltrimethoxysilane, 1H, 1H, 2H, 2H-perfluorodecyltrimethoxysilane and (3,3,3-trifluoropropyl)methyldimethoxysilane.
The concentration of coupling agents can be 0.2-1.2% by weight with respect to the base pigment.
A further feature is to provide a process for obtaining the pearl luster pigments of the invention.
This feature can be achieved by the provision of a multistage process in which the calcined, platelet-shaped substrate coated with one or more metal oxides is suspended in water, heated at from 25 to 100xc2x0 C., preferably from 40 to 80xc2x0 C., and adjusted to a pH of from 3 to 11, preferably from 5 to 9, in a first stage one or more water-soluble metal salts are added which correspond to the calcined metal oxides of the metal oxide coating of the platelet-shaped substrate, these salts are deposited in whole or in part as oxide, hydroxide and/or oxide hydrate, followed by heating at from 30 to 100xc2x0 C., preferably from 40 to 75xc2x0 C., and adjustment to a pH of from 3 to 9, preferably from 6 to 7, in a second stage a water-soluble silicate and/or aluminum salt is added, and is deposited in whole or in part as oxide, hydroxide and/or oxide hydrate, in a third stage, by adding at least one water-soluble silicate, aluminum salt, cerium salt and/or zirconium salt at a pH in the range from 3 to 9, preferably from 6 to 7, the corresponding oxides, hydroxides or oxide hydrates thereof are deposited, it being necessary for these to differ from those of the second stage, and in a fourth stage at least one organofunctional coupling agent is added and is deposited at a pH of from 3 to 9, preferably from 6 to 8.
As calcined platelet-shaped substrates coated with metal oxides it is possible to use the substrates already mentioned above with the abovementioned metal oxide coatings, which are available commercially under the designation Iriodin(copyright) (manufacturer: E. Merck, Darmstadt).
A suitable water-soluble silicate is preferably sodium silicate; suitable water-soluble aluminum salts, cerium salts and zirconium salts are, in general, all water-soluble salts of these metals, although the readily obtainable halides and halide hydrates, for example, are appropriate.
Organofunctional coupling reagents used are preferably those mentioned above.
The aftercoating process of the invention may be carried out as described above in one operation without isolating and working up the pigment after the first precipitation reaction (first stage). However, it is also possible to isolate the pigment after the first stage, i.e., after the application of the adhesion-promoting layer.
The pearl luster pigments coated in accordance with the invention are employed in particular in connection with the pigmenting of inks, such as printing inks, for example, and plastics, such as polymer films, for example, and also coating compositions, such as paints, for example. However, they are also employed in other areas in which the abovementioned improved properties play a part, such as in the pigmentation of cosmetics, for example.
Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The following preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever.
In the foregoing and in the following examples, all temperatures are set forth uncorrected in degrees Celsius; and, unless otherwise indicated, all parts and percentages are by weight.
The entire disclosure of all cited applications, patents and publications and of corresponding DE application No. 10054980.2, filed Nov. 6, 2000, is hereby incorporated by reference.